1. Field of the Invention
The present invention relates to a polyethylene glycol derivative comprising an arginine-glycine-aspartic acid tripeptide unit or glutamic acid-isoleucine-leucine-aspartic acid-valine-proline-serine-threonine (SEQ ID 00:1) octapeptide unit or salts thereof as well as a composition for inhibiting adhesion of animal cells and a composition for inhibiting c oagulation/cohesion of blood platelets.
2. Prior Art
Fibroncetin is a protein involved in the cell-extracellular substrate cohosion and is likewise thought to be involved in coagulation of blood platelets and the metastasis of cancer. These interactions are mediated by a series of receptors present in the cell surface region, it is confirmed that these receptors can specifically recognize an amino acid sequence: arginine-glycine-aspartic acid (hereinafter referred to as "Arg-Gly-Asp") of the fibronectin although the fibronectin is a macromolecule having a molecular weight of about 250,000 and there has been reported that the sequence plays an important role in the interaction between the receptors and the fibronectin (Nature, 309, 1984, p. 30). Since then, there have been conducted many studies in which an oligopeptide or polypetide having such an amino acid sequence: Arg-Gly-Asp is used.
There have been reported various studies, such as a method for inhibiting the coagulation of blood platelets by the use of various linear and cyclic oligopeptides having an Arg-Gly-Asp sequence (Polymer Preprints, Japan, 38, 1989, p. 3149; Japanese Unexamined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Hei 2-174797); a method in which a peptide having an Arg-Gly-Asp sequence is used as a cell movement-inhibiting agent (J.P. KOKAI No. Hei 2-4716); and a method using, as a cell-adhesive membrane, a PMMA film on which Arg-Gly-Asp sequences are immobilized (Polymer Preprints, Japan, 37, 1988, p. 705). In addition, J.P. KOKAI Nos. Hei 1-309682 and Hei 1-305960 disclose a method which comprises covalently bonding peptides having Arg-Gly-Asp sequences as essential structural units to a polymer and in which the resulting product is used as a substrate for cultivating animal cells or for biological composite artificial organs and J.P. KOKAI No. Sho 64-6217 discloses a method in which a polypeptide having Arg-Gly-Asp-Ser sequences is used as a platelet protective agent for blood taken out of the body. Further, there has been known a method comprising inhibiting the metastasis of cancer by the use of an oligopeptide having Arg-Gly-Asp sequences or a polypeptide having the sequence as repeating units (Int. J. Biol. Macromol., 11, 1989, p. 23; ibid, 11, 1989, p. 226; and Jpn. J. Cancer Res., 60, 1989, p. 722).
Moreover, it has recently been proved that cell-adhesive sequences other than the Arg-Gly-Asp are also present in the fibronectin molecule and one of these has become of major interest recently, which is a CSI peptide (comprising a glutamic acid-isoleucine-leucine-aspartic acid-valine-proline-serine-threonine sequence) (SEQ ID No: 1) present in the IIICS (type III homology connecting segment) region (J. Biol. Chem., 262, 1987, p. 6886). This peptide is recognized by the fibronectin receptor like the Arg-Gly-Asp peptide and has been thought to be involved in the adhesion specificity of the fibronectin. It has presently been proved that the minimum unit capable of exhibiting such adhesion activity is an octapeptide having a glutamic acid-isoleucine-leucine-aspartic acid-valine-proline-serine-threonine sequence (hereinafter abbreviated to as "EILDVPST") (SEQ ID No: 1) (J. Cell Biol., 107, 1988, p. 2189).
On the other hand, polyethylene glycol is an amphiphathic synthetic polymer having both hydrophilic and hydrophobic properties. There has been proposed a method for modifying the properties of enzymes by the use of polyethylene glycol (Trends in Biotech., 4, 1986, p. 68) and there has been succeeded in the modification of properties of various enzymes through the introduction of the enzymes into the polyethylene glycol derivatives. However, there has not yet been known a compound obtained by introducing an oligopeptide having an Arg-Gly-Asp sequence or a polypeptide having the sequences as repeating units into the polyethylene glycol derivative. It would be anticipated that the resulting compound has an improved ability of binding to receptors and an improved stability in the blood.